Problem 18 - Chemistry: The Central Science

Question

Complete and balance the following equations: (a) \(\mathrm{NaOCH}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) (b) \(\mathrm{CuO}(s)+\mathrm{HNO}_{3}(a q) \longrightarrow\) (c) \(\mathrm{WO}_{3}(s)+\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow}\) (d) \(\mathrm{NH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow\) (e) \(\mathrm{Al}_{4} \mathrm{C}_{3}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\)

Step-by-Step Solution

Answer

(a) \(\mathrm{NaOCH}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{NaOH}(s)+\mathrm{CH}_{3}\mathrm{OH}(l)\) (b) \(\mathrm{CuO}(s)+2\mathrm{HNO}_{3}(a q) \longrightarrow \mathrm{Cu(NO}_{3}\mathrm{)_{2}}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) (c) \(\mathrm{WO}_{3}(s)+3\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{W}(s)+3\mathrm{H}_{2} \mathrm{O}(g)\) (d) \(2\mathrm{NH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{N}_{2}(g)+2\mathrm{H}_{2} \mathrm{O}(l)\) (e) \(\mathrm{Al}_{4} \mathrm{C}_{3}(\mathrm{~s})+12\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow 4\mathrm{Al(OH)}_{3}(s)+3\mathrm{CH}_{4}(g)\)

Step 1: Identify the products

NaOCH3 reacts with water to produce sodium hydroxide (NaOH) and methanol (CH3OH).

Step 2: Write the unbalanced equation

\(\mathrm{NaOCH}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{NaOH}(s)+\mathrm{CH}_{3}\mathrm{OH}(l)\)

Step 3: Balance the equation

The equation is already balanced, so no changes are required. The balanced equation is: \(\mathrm{NaOCH}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{NaOH}(s)+\mathrm{CH}_{3}\mathrm{OH}(l)\) (b) To balance the given equation, follow these steps:

Step 4: Identify the products

CuO reacts with HNO3 to produce copper(II) nitrate (Cu(NO3)2) and water (H2O).

Step 5: Write the unbalanced equation

\(\mathrm{CuO}(s)+\mathrm{HNO}_{3}(a q) \longrightarrow \mathrm{Cu(NO}_{3}\mathrm{)_{2}}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\)

Step 6: Balance the equation

Adjust the coefficients to balance the equation: \(\mathrm{CuO}(s)+2\mathrm{HNO}_{3}(a q) \longrightarrow \mathrm{Cu(NO}_{3}\mathrm{)_{2}}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) (c) To balance the given equation, follow these steps:

Step 7: Identify the products

WO3 reacts with H2 to produce tungsten (W) and water (H2O) at high temperatures.

Step 8: Write the unbalanced equation

\(\mathrm{WO}_{3}(s)+\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{W}(s)+\mathrm{H}_{2} \mathrm{O}(g)\)

Step 9: Balance the equation

Adjust the coefficients to balance the equation: \(\mathrm{WO}_{3}(s)+3\mathrm{H}_{2}(g) \stackrel{\Delta}{\longrightarrow} \mathrm{W}(s)+3\mathrm{H}_{2} \mathrm{O}(g)\) (d) To balance the given equation, follow these steps:

Step 10: Identify the products

NH2OH reacts with O2 to produce nitrogen gas (N2) and water (H2O).

Step 11: Write the unbalanced equation

\(\mathrm{NH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{N}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l)\)

Step 12: Balance the equation

Adjust the coefficients to balance the equation: \(2\mathrm{NH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{N}_{2}(g)+2\mathrm{H}_{2} \mathrm{O}(l)\) (e) To balance the given equation, follow these steps:

Step 13: Identify the products

Al4C3 reacts with water to produce aluminum hydroxide (Al(OH)3) and methane (CH4).

Step 14: Write the unbalanced equation

\(\mathrm{Al}_{4} \mathrm{C}_{3}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Al(OH)}_{3}(s)+\mathrm{CH}_{4}(g)\)

Step 15: Balance the equation

Adjust the coefficients to balance the equation: \(\mathrm{Al}_{4} \mathrm{C}_{3}(\mathrm{~s})+12\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow 4\mathrm{Al(OH)}_{3}(s)+3\mathrm{CH}_{4}(g)\)

Key Concepts

Balancing Equations

Balancing chemical equations is a fundamental concept in chemistry, and it is essential for predicting the outcomes of chemical reactions. When a chemical reaction occurs, the substances involved, known as reactants, transform into new substances called products. A balanced chemical equation ensures that the same number of each type of atom appears on both sides of the equation. This is important because it reflects the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction.

To balance an equation, one must adjust the coefficients—the numbers placed before the chemical formulas—without altering the chemical formulas themselves. Here is a step-by-step approach to balancing equations:

• Identify the reactants and products in the chemical equation.
• Write their chemical formulas correctly.
• Count the number of atoms of each element in both the reactants and products.
• Adjust the coefficients to make the number of atoms of each element equal on both sides.

It often helps to start with more complex molecules first and leave simple molecules, like diatomic gases, to be balanced at the end. By following these steps, you can ensure that a chemical equation is properly balanced.

Reactants and Products

In every chemical reaction, there are substances known as reactants and products. Understanding these terms is key to making sense of chemical equations. Reactants are the starting substances that undergo change during the reaction. Their chemical identities are modified as a result of the process.

On the other hand, products are the substances formed from the reactants. They are the final outcome of the chemical transformation. For example, in a reaction like: \[\text{NaOCH}_3 + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{CH}_3\text{OH}\]The reactants are \(\text{NaOCH}_3\) and \(\text{H}_2\text{O}\) while the products are \(\text{NaOH}\) and \(\text{CH}_3\text{OH}\).

Each reaction has unique reactants and products, which means understanding the chemical nature of each is crucial for predicting the products of a reaction. Additionally, the state of each reactant and product (solid, liquid, gas) can impact how they react. In chemical equations, these states are usually indicated by letters in parentheses: (s) for solids, (l) for liquids, (g) for gases, and (aq) for aqueous solutions (substances dissolved in water).

Chemical Reactions

Chemical reactions involve the transformation of one or more substances into different substances via breaking and forming of bonds. They are at the heart of chemistry and are crucial for everything from breathing to energy production.

A chemical reaction can be categorized in various ways, such as synthesis, decomposition, single replacement, and double replacement reactions, depending on the types of changes occurring. For instance, in synthesis reactions, multiple reactants combine to form a single product, while in decomposition reactions a single compound breaks down into multiple compounds or elements.

Understanding the driving forces of reactions is also vital:

• Energy changes, where reactions might require energy absorption (endothermic) or release energy (exothermic).
• The need to achieve a more stable electron configuration, such as forming a full outer electron shell.
• Formation of a gas, precipitate, or a neutralization in acid-base reactions.

These underlying principles help predict whether a reaction will occur and the nature of the products. Chemical reactions follow predictable patterns and can be represented effectively through balanced chemical equations, combining their symbolic and quantitative aspects to describe changes accurately.